循环电载荷下大功率LED金引线疲劳断裂寿命预测

随着大功率发光二极管（LED）在照明领域的普及与广泛应用,可靠性逐渐成为研究的重点。大功率LED封装器件中金引线疲劳断裂失效一直是制约其可靠性的重要因素。通过针对大功率LED封装器件中的金引线力学仿真与功率循环试验相结合的方法,首先确定循环电载荷条件下该型LED的主要失效原因为金引线疲劳断裂,其次提出基于电流加速模型的加速因子提取方法和基于应变幅值的Coffin-Manson解析寿命预测方法,最终完成对LED金引线疲劳断裂寿命的预测和试验验证。研究结果表明:所提方法具有较高的寿命预测精度,可以满足大功率LED封装器件可靠性快速、准确评估的要求。      

Influence of pre-tension on ballistic impact performance of multi-layer Kevlar 49 woven fabrics for gas turbine engine containment systems

In this paper, ballistic impact tests on wrapped multi-layer Kevlar 49 woven fabric systems were carried out with a flat blade projectile to investigate the impact response during a fan blade out event. The influences of the number of Kevlar layers and pre-tension were discussed particularly. Test results were used to analyze failure modes and energy absorption characteristics of multi-ply Kevlar fabrics. Results show that there are two kinds of impact damage for fabrics: global deformation mainly involving stretching of yarns in the impact region and fabric wrinkle from both sides to the impact zone, and local damage characterized by yarn fracture, yarn pull-out, and yarn unraveling. The energy absorption capability of Kevlar 49 woven fabrics improves with the number of fabric layers. The energy absorbed by multi-layer fabrics increases slightly at the beginning and then decreases substantially with pre-tension. The work in this paper can provide guidance for designing light-weight multi-layer fabrics containment systems.     

利用疲劳裂纹扩展速率估算断裂韧性

提出了一种利用疲劳裂纹扩展速率来估算断裂韧性的方法,并利用2种材料12组试验数据对该法产生的误差及其控制方法进行了分析研究,结果表明,其误差可以控制在试验分散带内。     

某型飞机断裂谱的低载截除

研究了截除低载对全机结构各部位裂纹扩展寿命的影响,导出寿命误差与裂纹扩展比的关系,并指出寿命误差主要取决于开裂结构的材料参数,而开裂部位的影响则可忽略不计。     

Al－Al_3Ni自生复合材料的高周疲劳损伤断裂机制及其应力比的影响

实验观察和研究了Ａｌ－Ａｌ３Ｎｉ自生复合材料的高周疲劳损伤断裂行为以及应力比Ｒ的影响,结果显示在Ｒ＝－１疲劳过程中孔洞沿界面区基体的优先萌生、联接和扩展是其损伤断裂的主要机制;并且发现Ｒ对疲劳寿命及断裂过程有明显影响,当Ｒ＝０时滑移带裂纹生长相对容易,寿命减小,而Ｒ＝∞时,裂纹集中在类似于压缩变形的宏观形变带内发展,寿命很长     

结构破坏危险率与使用寿命的关系

在结构疲劳寿命服从双参数Ｗｅｉｂｕｌ分布假设的基础上,通过结构细节疲劳额定值的概念给出了结构破坏危险率与使用寿命的关系式,并通过实例计算得出了破坏危险率－寿命曲线。     

着陆缓冲装置特性分析及控制方法研究

着陆缓冲技术在航天器回收系统中的应用日益广泛,文章对着陆缓冲过程所使用的两种发动机推力制度进行了比较;分析了着陆缓冲过程中影响系统最终性能的因素。认为影响最大的因素是初始条件和环境条件的改变,对此提出了一种较为实用的控制方法。应用这一方法,可以最大限度地消除初始条件和环境条件的改变对着陆缓冲装置性能的影响。     

断口反推技术在飞机结构损伤容限中的应用

本文以某机翼疲劳试验时下壁板油泵口边缘螺栓孔实测裂纹扩展数据为例,对断口反推方法、原理进行了探讨,对其在疲劳损伤容限方面用来确定裂纹扩展周期、裂纹扩展曲线以及确定初始裂纹长度等方面的应用做了进一步深入分析、论证,并提出了自己的见解。     

混杂复合材料层合板抗冲击性能研究

为了探究复合材料层合板在实际应用中因承受冲击载荷而造成的结构安全问题,本研究采用实验和仿真相结合的方法,首先探究冲头形状对复合材料层合板损伤机理的影响,然后结合不同冲击能进一步揭示层合板的承载力和能量吸收变化规律。结果表明,相同冲击能下,层合板的损伤范围和承载力随着圆锥头、半球头、平头依次增加;相应的层合板的临界穿透能量随着圆锥头、半球头、平头依次增大;冲头形状和冲击能对层合板的吸能能力有较大的影响。     

An adaptive fast fixed-time guidance law with an impact angle constraint for intercepting maneuvering targets

Sliding mode guidance laws based on a conventional terminal sliding mode guarantees only finite-time convergence, which verifies that the settling time is required to be estimated by selecting appropriate initial launched conditions. However, rapid convergence to a desired impact angle within a uniform bounded finite time is important in most practical guidance applications. A uniformly finite-time/fixed-time convergent guidance law means that the convergence (settling) time is predefined independently on initial conditions, that is, a closed-loop convergence time can be estimated a priori by guidance parameters. In this paper, a novel adaptive fast fixed-time sliding mode guidance law to intercept maneuver targets at a desired impact angle from any initial heading angle, with no problems of singularity and chattering, is designed. The proposed guidance law achieves system stabilization within bounded settling time independent on initial conditions and achieves more rapid convergence than those of fixed-time stable control methods by accelerating the convergence rate when the system is close to the origin. The achieved acceleration-magnitude constraints are rigorously enforced, and the chattering-free property is guaranteed by adaptive switching gains. Extensive numerical simulations are presented to validate the efficiency and superiority of the proposed guidance law for different initial engagement geometries and impact angles.